Stereo-examination systems and stereo-image generation apparatus as well as a method for operating the same

ABSTRACT

A stereo-examination system for imaging an object  8  is proposed, comprising an objective arrangement  3  having an optical axis  5  and an object plane  7  for positioning the object  8  to be imaged, wherein the objective arrangement  3  receives an object-side beam bundle  11  emanating from the object plane  7  into a solid angle region  9  and converts the same into an image-side beam bundle  13 , a selection arrangement for selecting at least a pair of partial beam bundles  19, 20  from the image-side beam bundle  13 , and an image transmission apparatus  51, 52  for generating a representation of images of the object  8  provided by the partial beam bundles  19, 20.    
     The stereo-examination system is distinguished in that the selection arrangement is provided for displacing a beam cross-section of at least one of the two partial beam bundles  19, 20  relative to a beam cross-section of the image-side beam bundle  13 , a controller  49  being provided for controlling the selection arrangement to displace the beam cross-section of the at least one partial beam bundle  19, 20  in circumferential direction about the optical axis  5.

[0001] The invention relates to a stereo-examination system for imagingan object, a stereo-image generation apparatus for generating at least apair of images of an object and a method for generating such images.

[0002] The system and the method according to the invention serve togenerate stereoscopic images and representations, respectively, of anobject such that, when viewing the images, the observer obtains athree-dimensional impression of the object. To this end, it is requiredfor the left eye and the right eye of the observer to perceive differentimages from different directions of view onto the object.

[0003] An example of a conventional stereo-examination system is astereomicroscope. A beam path of a conventional stereomicroscope isschematically shown in FIG. 1. The stereomicroscope 1 shown therecomprises an objective 3 with an optical axis 5 and an object plane 7 inwhich an object to be viewed is positioned. A beam bundle 11 emanatingfrom the object or object plane 7 into a solid angle region 9 around theoptical axis 5 images the objective 3 to infinity and thus converts itinto a parallel image-side beam bundle 13. Two zoom systems, each havingan optical axis 17 and 18, respectively, of its own, are positionedadjacent each other in the parallel beam bundle 13 such that the opticalaxes 17 and 18 of the zoom systems are offset parallel to the opticalaxis 5 of the objective 3 and spaced apart from each other by a distancea. The two zoom systems 15, 16 each feed a partial beam bundle 19 and20, respectively, out of the parallel beam bundle 13, the partial beambundle 19 being supplied to a left eye 21 of a user and the otherpartial beam bundle 20 being supplied to a right eye 22 of the user. Tothis end, a field lens 23, a prism system 25 and an ocular 27 aredisposed in the beam path of each partial beam bundle 19, 20. As aresult, the left eye 21 perceives the object 7 at a viewing angle α withrespect to the optical axis 5, while the right eye 22 perceives theobject at a viewing angle −α with respect to the optical axis. As aresult, the user gets a stereoscopic, three-dimensional impression ofthe object.

[0004]FIG. 2 shows part of a beam path of a conventional microscope 1for providing a stereoscopic image of an object for each one of twousers. Similar to the microscope shown in FIG. 1, an objective 3produces a parallel image-side beam bundle from a beam bundle 11emanating from the object into a solid angle region, with two zoomsystems 15 and 16 being provided, each feeding a partial beam bundle 19and 20, respectively, out of the parallel beam bundle which are suppliedvia field lenses 23 as well as prism systems and oculars, not shown inFIG. 2, to the two eyes of a first observer.

[0005] In the parallel image-side beam path, there are further disposedtwo mirrors 31 which feed two further partial beam bundles 33 and 34 outof the parallel beam path and reflect the same such that they extendtransversely to the beam direction of the partial beam bundles 19, 20.These two partial beam bundles 33 and 34 are each supplied, via a zoomsystem 35 and 36, respectively, as well as prism systems and oculars,not shown in FIG. 2, to the two eyes of a second observer.

[0006] In order for this microscope to be used by two observers, it isrequired that, while observing the object, the two observers areconstantly in a fixed spatial position relative to the microscope. Inparticular, if the microscope is used as surgical microscope during asurgical operation, this spatial limitation is obstructive for the twoobservers who must operate as surgeons in the operating field.

[0007] Accordingly, it is an object of the present invention to providea stereo-examination system and a stereo-image generation apparatuswhich provide degrees of freedom at least for one observer as regardshis position relative to the object to be viewed.

[0008] According to a first aspect, the invention proceeds from astereo-examination system for imaging an object, or an intermediateimage produced from the object, comprising an objective arrangement withan optical axis and an object plane in which the object to be imaged, orthe intermediate image, is positioned. The objective arrangementreceives an object-side beam bundle emanating from the object, orintermediate image, into a solid angle region and converts the same intoan image-side beam bundle. A selection arrangement selects or feeds atleast a pair of partial beam bundles out of said image-side beam bundlewhich are supplied to an image transmission apparatus to generate arepresentation of the image information contained in each one of thepartial beam bundles.

[0009] The stereo-examination system is distinguished in that itcomprises a selection arrangement which is provided to displace a beamcross-section of at least one of the two partial beam bundles relativeto a beam cross-section of the image-side beam bundle, i.e., to changethe position of the beam cross-section of the fed-out partial beambundle within the beam cross-section of the image-side beam bundle.

[0010] To this end, the stereo-examination system comprises a controllerfor controlling the selection arrangement such that it displaces thebeam cross-section of the at least one partial beam bundle relative tothe beam cross-section of the image-side beam bundle in circumferentialdirection about the optical axis. As a result, it is possible toeliminate and modify the fixed arrangement, as it is known from theprior art, of the fed-out partial beam bundle in circumferentialdirection about the optical axis of the object such that representationsof the object can be supplied to the observer via the displaced partialbeam bundles, said representations being generated from different,variable viewing angles. It is thus possible for the observer to move inazimuthal direction about the object and, when the selection arrangementis controlled accordingly, to view stereoscopic images of the object atdifferent azimuth angles.

[0011] Preferably, the selection arrangement is provided to selectivelychoose only a first one or a second one of the pair of partial beambundles from the image-side beam bundle. As a result, the individualpartial beam bundles can be imaged, successively in time, by the imagetransmission apparatus. It is thus particularly easy to spatiallyseparate the individual partial beam bundles from each other. Thisapplies, in particular, if several pairs of partial beam bundles are fedout of the image-side beam cross-section for several observers.

[0012] Preferably, such a selection arrangement is provided asswitchable stop which selectively transmits the first one or the secondone of the partial beam bundles or still further partial beam bundles.

[0013] To this end, the switchable stop preferably comprises a pluralityof separately controllable stop elements, each of which is switchablefrom a state in which they transmit much or substantially all light to astate in which they transmit less light or substantially no light. Thestop elements are then controlled such that they are light-permeable inthe region of the beam cross-section of the image-side beam bundle inwhich the respective partial beam bundle is to be shaped andlight-impermeable in the remaining region of the image-side beam bundle.Subsequently, the stop elements are then switched into thelight-permeable state in another region of the image side beam-crosssection in order for the other partial beam bundle to be shaped there.

[0014] The switchable stop elements may be formed of liquid crystals ormechanically displaceable stop elements.

[0015] As an alternative to the provision of the selection arrangementas switchable stop, it can also be provided in the form of a switchablemirror disposed in the cross-section of the image-side beam bundle forselectively reflecting the first one or the second one of the partialbeam bundles or further beam bundles. The beam bundles are then formedby reflection at reflection regions of the switchable mirror. To thisend, the mirror preferably comprises separately controllable mirrormembers which are switchable from a state in which the light of theimage-side beam bundle is reflected towards the image transmissionapparatus to a corresponding non-reflecting or less reflecting state.

[0016] Preferably, the mirror members comprise liquid crystals ormechanically displaceable mirror elements.

[0017] The plurality of partial beam bundles successively fed out of theimage-side beam bundle by the selection arrangement are preferablysupplied to a common camera which is controlled by the controller suchthat it generates, successively in time, representations of the imageinformation which is contained in the individual partial beam bundles.

[0018] Here, it is in particular possible to generate with one camerastereo-image pairs for several observers which are located at differentpositions in circumferential direction about the optical axis of theobjective.

[0019] Alternatively, it is also provided for that, in order to generateeach stereo-image pair, a pair of cameras is provided, each camera beingallocated to a separate partial beam bundle. It is then possible toobtain simultaneously representations of the image information containedin the two partial beam bundles.

[0020] In this respect, it is provided for the two cameras to be jointlydisplaceable together with the two partial beam bundles. To this end,the cameras are connected to each other in rotationally fixed positionwith respect to a rotational axis, but can be jointly rotated about thesame.

[0021] As an alternative thereto, it is provided for that the twocameras are stationary relative to the objective arrangement, and theselection arrangement comprises an optical system which is rotatableabout a rotational axis in order to supply the two partial beam bundleswhich are displaceable about the optical axis to the two stationarycameras.

[0022] Preferably, the rotational optical system is an image-rotatingoptical system so that both cameras can directly generate the respectiverepresentations in correct image orientation.

[0023] Preferably, the rotational optical system comprises a Dove prismor a Schmidt-Perchan prism.

[0024] If the examination system is provided for use by severalobservers, it comprises preferably a beam-dividing arrangement to dividethe image-side beam bundle and to supply it to several selectionarrangements. In this case, a separate image transmission apparatus isallocated to each selection arrangement for respectively generating thestereoscopic representations for one observer.

[0025] If use is made of a beam-dividing arrangement, it offers a simplepossibility to illuminate the object in that an illuminating light beamis fed into the beam path through the beam-dividing arrangement suchthat the illuminating light beam passes through the objective and isfocused by the same onto the object.

[0026] Furthermore, it is provided for that the image transmissionapparatus comprises at least three cameras, each of which receives aportion of the image-side beam bundle in fixed spatial relation relativeto each other and generates a representation of the image informationcontained in the partial beam bundles supplied to the same. Theselection arrangement then selects a pair of cameras from the at leastthree cameras to combine the representations thereof to a stereoscopicrepresentation.

[0027] By selecting different camera pairs, partial beam bundles arethus selected for generating the representations which are differentlypositioned about the optical axis of the objective.

[0028] Preferably, the objective is provided such that it images theimage-side beam bundle substantially to infinity and thus converts it toa substantially parallel beam bundle. However, the objective can alsoimage to finity and form a convergent image-side beam bundle in whichthe selection arrangement is provided.

[0029] Preferably, the selection arrangement selects the partial beambundles at a location of the image-side beam path where a Fourier planeis disposed.

[0030] Preferably, the image transmission comprises a display apparatusfor representing the image information contained in the two partial beambundles such that the image information of a first partial beam bundleof the pair of partial beam bundles is visible for the left eye of theobserver and, correspondingly, the representation of the imageinformation contained in the other, second partial beam bundle of thepair is visible for the right eye of the observer. The imagetransmission apparatus may comprise a viewing screen suitable for astereoscopic image observation. For example, this may be a viewingscreen which presents the two representations, successively in time, tothe observer, the latter wearing shutter spectacles which aresynchronized with said time sequence and alternately give the left eyeand the right eye the view over the display screen. It is also possiblefor a separate image transmission apparatus to be allocated to each eyeof the observer which is, in particular, worn directly on the head ofthe observer in front of the eye.

[0031] When neccessary for a correct stereo representation, the imagesare rotated by the image transmission apparatus about an image rotationangle such that the image rotation angle increases with increasingdisplacement of the partial beam bundles about the optical axis.

[0032] Preferably, the examination system then comprises a positiondetection apparatus to detect an azimuth position of the observerrelative to the objective arrangement, the controller then using thedetected azimuth position to adjust the displacement of thecross-sections of the two partial beam bundles relative to the beamcross-section of the image-side beam bundle in circumferential directionabout the optical axis. The examination system can then supplystereoscopic representations to the observer from a perspective whichcorresponds to the perspective from which the observer would view theobject directly, i.e., without the use of the objective arrangement.

[0033] Embodiments of the invention will now be described in furtherdetail with reference to the drawings, wherein

[0034]FIG. 1 shows a beam path of a conventional stereomicroscope;

[0035]FIG. 2 shows a part of a beam path of a further conventionalstereomicroscope for two observers,

[0036]FIG. 3 shows an embodiment of a stereo-examination systemaccording to the invention comprising several rotatable cameras,

[0037]FIG. 4 is a schematically representation from the side of afurther embodiment of a stereo-examination system according to theinvention comprising several rotatable cameras,

[0038]FIG. 5 is a plan view of the stereo-examination system shown inFIG. 4,

[0039]FIG. 6 shows an embodiment of a stereo-examination systemaccording to the invention with stationary camera and rotatable opticalsystem,

[0040]FIG. 7 shows a further embodiment of a stereo-examination systemaccording to the invention with rotatable cameras,

[0041]FIG. 8 shows a further embodiment of a stereo-examination systemaccording to the invention with stationary cameras and rotatable opticalsystems,

[0042]FIG. 9 shows a still further embodiment of a stereo-examinationsystem according to the invention with stationary cameras and rotatableoptical systems,

[0043]FIG. 10 shows a still further embodiment of a stereo-examinationsystem according to the invention with stationary cameras and rotatableoptical systems

[0044]FIG. 11 is a schematic plan view of an embodiment of thestereo-examination system according to the invention comprising an imagetransmission apparatus with eight cameras,

[0045]FIG. 12 shows an embodiment of a stereo-examination systemaccording to the invention comprising a switchable stop,

[0046] FIGS. 13 to 16 show variants of the switchable stop shown in FIG.13,

[0047]FIG. 17 shows an embodiment of a stereo-examination systemaccording to the invention comprising a switchable mirror arrangement,

[0048]FIG. 18 is a schematic representation of the stereo-examinationsystem according to the invention together with a user,

[0049]FIG. 19 is a plan view of stereobasis of the examination systemshown in FIG. 18,

[0050]FIG. 20 shows a position detection apparatus for use in thestereo-examination system shown in FIG. 18,

[0051]FIG. 21 shows a further embodiment of a stereo-examination systemaccording to the invention,

[0052]FIG. 22 shows an illumination system for use in astereo-examination system shown in FIGS. 1 to 19,

[0053]FIG. 23 is a cross-sectional view for illustrating the function ofthe illumination system shown in FIG. 22,

[0054] FIGS. 24 to 30 show further embodiments of a stereo-examinationsystem according to the invention.

[0055] An embodiment of a stereo-examination system according to theinvention is schematically shown in FIG. 3. The stereo-examinationsystem 1 comprises an objective 3 with an optical axis 5 and an objectplane 7. An object 8 is positionable in the object plane 7. Anobject-side beam bundle 11 emanates from the object 8 or object plane 7into a solid angle region 9 and is received by the objective 3 to beimaged to infinity and converted into a parallel image-side beam bundle13, respectively, the optical axis 5 being disposed in a center of abeam cross-section of the image-side beam bundle 13.

[0056] Behind the objective 3, there is positioned a beam divider 41 inthe beam path comprising a semi-transparent mirror surface 43 disposedat 450 to the optical axis 5. The beam divider 41 serves to divide theparallel image-side beam bundle into two portions 13′ and 13″, the beamportion 13′ passing straightly through the beam divider 41 and the beamportion 13″ emerging from the beam divider 41 at 90° to the optical axis5.

[0057] After the beam divider 41, there are positioned two zoom systems15 and 16 in the beam path of the image-side beam bundle 13′, each ofsaid zoom systems 15 and 16 having an optical axis 17 and 18,respectively, of its own. The optical axes 17 and 18 of the zoom systems15 an 16 extend parallel to the optical axis 5. Furthermore, the zoomsystems 15 and 16 are disposed symmetrically with respect to the opticalaxis 5 of the objective 3 and are spaced apart from each other by adistance a. Due to the geometric dimensions of the entrance lenses ofthe zoom systems 15, 16, only a portion of the radiation supplied by theimage-side beam bundle 13′ enters the zoom systems. These partial beambundles 19 and 20 entering the zoom systems 15 and 16, respectively, aresupplied by the zoom systems 15 and 16 to cameras 45 and 46 which are,for example, CCD cameras. Here, the camera 45 is fixedly allocated tothe zoom system 15, and the camera 46 is fixedly allocated to the zoomsystem 16.

[0058] When extending the partial beam bundles 19, 20 entering the zoomsystems 15 and 16 back to the object 8, it is evident that the camera 46receives an image of the object 8 as it appears upon observation of theobject 8 at a viewing angle α with respect to the optical axis 5 of theobjective. Accordingly, the camera 45 receives an image of the object 8as it appears upon observation of the object 8 at a viewing inclined atan angle a with respect to the optical axis 5. However, the viewingangles of the two images produced by the two cameras 45, 46 differ by avalue of 2 a. The images recorded by the cameras 45, 45 are digitallyread out by a controller 49 and either stored or directly supplied totwo displays 51 and 52, the display 51 representing the image receivedfrom the camera 45 and the display 52 representing the image receivedfrom the camera 46. The displays 51, 52 may be provided in the form ofhead-mounted display units worn on the head of a user, so that thedisplay 51 is viewed by the left eye of the user and the display 52 isviewed by the right eye of the user. Accordingly, the left eye receivesan image of the object 8 as it is generated upon observation of theobject 8 inclined at an angle α to the optical axis 5, and the right eyeof the user receives an image of the object as it is generated uponobservation of the object 8 at a viewing angle α opposite thereto. Asimages of the same object but at different viewing angles are presentedto the eyes of the user, the two images are a stereo-image pair, i.e., apair of images which evokes a stereoscopic three-dimensional impressionof the object 8 on the part of the user.

[0059] The two cameras 45, 46 and the two zoom systems 15, 16 arefixedly mounted in a common holder 53 which is rotatable about theoptical axis 5 (see angle φ in FIG. 3). A motor 55 driven by thecontroller 49 is provided for driving the holder 53 together with thezoom systems 15 and 16 and the cameras 45, 46. By actuation of the motor55, the zoom systems 15, 16 and the cameras 45, 46 are rotated about theoptical axis 5 of the objective 3. As a result, the partial beam bundles19, 20 supplied to the cameras 45, 46 are also displaced relative to thebeam cross-section of the parallel image-side beam bundle 13′. As aresult, the directions of view onto the object 8 of the images of theobject 8 presented on the displays 51 and 52 change as well. Althoughthe angle 2α between the partial beam bundles imaged on the cameras 45,46 is maintained, the partial beam bundles supplied to the cameras 45,46 have been displaced in azimuthal direction (see angle φ in FIG. 3)about the optical axis 5, i.e., a stereobasis for the stereoscopicobservation of the object has rotated about the optical axis 5 ascompared to the situation shown in FIG. 3.

[0060] Preferably, the magnifying powers of the zoom systems 15, 16 arethe same.

[0061] Accordingly, the stereo-examination system 1 can presentstereoscopic image pairs to the user of the same as they are producedupon observation of the object 8, with a circumferential angle φ orazimuth of the stereobasis being freely adjustable by the controller 49.Methods for adjusting the azimuth by the controller 49 are describedbelow.

[0062] The beam portion 13″ of the image-side beam bundle extendingalong a mirrored optical axis 5′ at 90° to the optical axis 5 of theobjective 3 impinges on two zoom systems 15′ and 16′ disposed parallelto the mirrored optical axis 5′, said zoom systems feeding two partialbeam bundles 19′ and 20′ out of the beam bundle 13″ and supplying thesame to two cameras 45′ and 46′. The images recorded by the cameras 45′,46′ are likewise read out by the controller 49 and presented on displays51′ and 52′, one display 51′ being allocated to the camera 45′ and theother display 52′ being allocated to the camera 46.

[0063] The two displays 51′ and 52′ are provided for observation by afurther user who is different from the user observing the displays 51and 52.

[0064] The cameras 45′ and 46′, too, are mounted together with the zoomsystems 15′ and 16′ on a holder 53′ and rotatable about the mirroredoptical axis 5′. To this end, a motor 55′ controlled by the controller49 is provided. Accordingly, the controller 49 can also adjust theazimuth for the stereobasis with which the further user observes theobject 8. In particular, the azimuths of the stereobases of the twousers are adjustable independently from each other.

[0065] Preferably, the magnifying power of the zoom systems 15′ and 16′is adjustable independently from the magnifying power of the zoomsystems 15 and 16.

[0066] In the following, variants of the stereo-examination systemillustrated in FIG. 3 are described. Components which correspond to eachother in structure and function are indicated by the same referencenumbers as in FIGS. 1 to 3. For the purpose of distinction, they are,however, supplemented by an additional letter. For the purpose ofillustration, reference is taken to the entire above description.

[0067]FIG. 4 is a side view and FIG. 5 a plan view of a furtherstereo-examination system 1 a.

[0068] The stereo-examination system la again comprises an objective 3 awith an optical axis 5 a and an object plane 7 a for positioning anobject 8 a. A beam bundle 11 a emanating from the object 8 a isconverted by the objective 3 a into a parallel image-side beam bundle 20a which enters a first beam divider 41 a and is divided by asemi-reflective mirror 43 a disposed at 45° to the optical axis 5 a intoa beam portion 13 a′ extending along a mirrored optical axis 5 a′ whichextends at 90° to the optical axis 5 a of the objective 3 a and a beamportion 13 a″ passing straightly through the first beam divider 41 a.The beam portion 13 a″ passing through the first beam divider enters asecond beam divider 41 a′ and is reflected at 90° by a semi-reflectivemirror 43 a′ disposed at 45° to the optical axis 5 a so that it extendsas mirrored beam portion 13 a″ along a mirrored optical axis 5 a″.

[0069] The examination system 1 a further comprises a lamp disposed onthe optical axis 5 a of the objective 3 a, the light emitted from saidlamp being shaped by means of a collimator 60 to form a parallel beambundle 61 which successively passes through the second beam divider 41a′ and the first beam divider 41a and subsequently the objective 3 a inorder to be shaped by the same to form a convergent beam forilluminating the object 8 a.

[0070] The beam divider 41 a (41 a′) is fixedly connected to a holder 53a (53 a′) which is supported to be rotatable about the optical axis 5 aof the objective 3 a, a motor, not shown in FIGS. 4 and 5, beingprovided to drive the same about the optical axis 5 a. Moreover, theholder 53 a (53 a′) supports a pair of zoom systems 15 a, 16 a (15 a′,16 a′) and a pair of cameras 45 a, 46 a (45 a′, 46 a′), each beingsymmetrically disposed with respect to the mirrored optical axes 5 a′ (5a″).

[0071] The zoom systems 15 a, 16 a (15 a′, 16 a′) transmit partial beambundles 19 a, 20 a (19 a′, 20 a′) to the cameras 45 a, 46 a (45 a′, 46a′) which, in the plan view of FIG. 5, are disposed adjacent one anotherand spaced apart from the mirrored optical axis 5 a′ (5 a″).

[0072] The zoom systems 15 a, 16 a, 15 a′, 16 a′ thus feed partial beambundles 19 a, 20 a, 19 a′, 20 a′ out of the parallel beam bundles 13 a′,13 a″, the arrangement of said partial beam bundles in the beamcross-section of the parallel beam bundle 13 a being particularlyevident from the plan view of FIG. 5. The partial beam bundles 19 a, 20a and 19 a′, 20 a′ form the stereobasis for the stereoscopicrepresentations of the object produced by the cameras 45 a, 46 a and 45a′, 46 a′, respectively, for observation by a first and a second user,respectively. By rotating the holders 53 a and 53 a′ about the opticalaxis 5 a, the stereobasis can be rotated about the optical axis 5 a foreach user such that each user can observe the object with different andindividually adjustable azimuths of his stereobasis.

[0073] A stereo-examination system 1 b shown in FIG. 6 comprises anobjective 3 b which converts a divergent beam bundle 11 b emanating fromthe object 8 b into a parallel image-side beam bundle 13 b. A zoomsystem 15 b is disposed in the parallel beam bundle 13 b. After havingpassed through the zoom system 15 b, the parallel beam bundle 13 benters a beam divider 41 b which comprises a semi-transparent mirror 42b to divide the parallel beam bundle 13 b into a parallel beam bundle 13b′ propagating further along an optical axis 5 b of the objective 3 band a parallel beam bundle 13 b″ extending at 90° to the optical axis 5b of the objective 3 b.

[0074] The parallel beam bundle 13 b′ propagating further along theoptical axis 5 b of the objective 3 b enters an image-rotating opticalsystem provided as Schmidt-Perchan prism 61 and emerges from the sameagain as parallel beam bundle 63. Disposed in the beam path behind theimage-rotating optical system 61, there is disposed a pair of cameras 45b, 46 b adjacent each other in the parallel beam bundle 63, each camerafeeding a partial beam bundle 19 b and 20 b, respectively, out of thebeam bundle 63.

[0075] The two cameras 45 b and 46 b and the beam divider 41 b arefixedly positioned with respect to the objective 3 b. However, theimage-rotating optical system 61 is disposed to be rotatable about theoptical axis 5 b. When the optical system 61 is rotated by an angle φabout the optical axis 5 b, the beam bundle 63 emerging from theimage-rotating optical system 61 is thus rotated relative to theparallel beam bundle 13 b′ entering the image-rotating optical system byan angle 2×φ about the optical axis 5 b. As a result, an azimuth of thestereobasis of the stereoscopic representations produced by the cameras45 b, 46 b can be rotated about the optical axis 5 b by rotation of theimage-rotating optical system 61 about the optical axis 5 b, whichrotation is caused by means of a motor, not shown in FIG. 6, via thecontroller, likewise not shown, of the examination system 1 b.

[0076] A system comprising an image-rotating optical system 61′ andcameras 45 b′ and 46 b′, corresponding to the system of image-rotatingoptical system 61 and cameras 45 b, 46 b, is disposed along the mirroredoptical axis 5 b′ and serves to generate stereoscopic representations ofthe object 8 b for a second user. For this user, too, an azimuth of thestereobasis can be changed for observation of the object 8 b byactuation of a drive, not shown in the Figure, to rotate theimage-rotating optical system 61′ about the axis 5 b′.

[0077] A stereo-examination system 1 c perspectively shown in FIG. 7again comprises an objective 3 c which converts a divergent beam bundle11 c emanating from an object 8 c into a parallel beam bundle 13 c. Fourcameras 45 c, 46 c, 45 c′ and 46 c′ are disposed in the parallel beambundle 13 c, each one of the four cameras feeding another partial beambundle 19 c, 20 c, 19 c′ and 20 c′ out of the parallel beam bundle. Therepresentations of the object 8 c generated by the cameras 45 c and 46 care supplied to the eyes of a first user via a controller, not shown inFIG. 7, and the images generated by the pair of cameras 45 c′ and 46 c′are presented to the eyes of a further user.

[0078] The cameras of the pair of cameras 45 c, 46 c are fixedlyconnected to each other by means of a rod 53 c and cameras of the pairof cameras 45 c′, 46 c′ are likewise fixedly connected to each other bymeans of a further rod 53 c′. The two cameras 45 c, 46 c are supportedby a sleeve 67 connected to the rod 53 c, while the cameras 45 c′ and 46c′ are supported by a rod 68 traversing the sleeve 67 which is connectedto the rod 53 c. Both the sleeve 67 and the rod 68 are supported to berotatable about an optical axis 5 c of the objective 3 c, with toothedwheels 69 and 70 being provided for the same to be driven on the sleeve67 and rod 68, respectively. The toothed wheels 69 and 70 are inengagement with a drive, not shown in FIG. 7, to rotate the camera pairs45 c, 46 c and 45 c′, 46 c′, respectively, in azimuth direction aboutthe optical axis 5 c. The camera pairs are independently rotatable aboutthe optical axis 5 c, the rotational angles, however, not being fullyfree, but rather limited by the cameras getting in abutment against eachother.

[0079] A stereo-examination system 1 d shown in FIG. 8 for generatingstereoscopic image pairs for two observers is similar in construction tothe examination system shown in FIG. 6. It likewise comprises two pairsof cameras 45 d, 46 d and 45 d′, 46 d′, respectively, which are fixedlypositioned with respect to an objective 3 d. Image-rotating opticalsystems 61 d and 61 d′ are respectively disposed between a beam divider41 d and the camera pairs. In contrast to the embodiment shown in FIG.6, the image-rotating optical system 61 d, 61 d′ is not provided asSchmidt-Perchan prism, but comprises a plurality of mirror surfaces 71,72, 73 and 74 which are disposed fixedly relative to each other androtatably about the optical axes 5 d′ and 5 d″, respectively. Moreover,a stationary mirror 75 is allocated to each camera which feeds thepartial beam bundle produced by the mirror system 61 d into therespective camera. The image pairs generated by the camera pairs areagain stereo-image pairs which present the object 8 d stereoscopicallyto a respective observer. By actuating a drive, not shown in FIG. 8, ofthe mirror systems 61 d, 61 d′, the azimuths of the stereobases for therespective observer are then rotatable about the optical axis 5 d.

[0080] A stereo-examination system 1 e schematically shown in FIG. 9again serves to generate stereo-image pairs for two observers. Theexamination system 1 e is substantially similar to the examinationsystem shown in FIG. 6, but differs from the same as far as thestructure of an image-rotating optical system 61 e is concerned. Thelatter comprises two prism systems 77 and 78 which are rotatablerelative to each other and about an optical axis 5 e. The two prismsystems 77 and 78 are driven by a gear system 79 to rotate about theoptical axis 5 e such that the prism system 78 rotates through an angleof 2×φ, while the prism system 77 rotates through an angle φ. The prismsystem 78 is disposed between a beam divider 41 e and the prism system77. It comprises two prisms 79 for moving two partial beam bundles 19 eand 20 e, which have been fed out of a parallel beam bundle 13 eproduced by an objective 3 e and are spaced apart from each other by arelatively large distance a from the optical axis 5 a, closer to theoptical axis 5 a. After having passed through the prism system 78, thepartial beam bundles 19 e, 20 e enter the prism system 77 whichcomprises an image-rotating Dove prism 80. As the partial beam bundles19 e, 20 e then extend relatively close to the optical axis, the Doveprism 80 can be of relatively small size. After having passed throughthe prism system 77, the partial beam bundles 19 e, 20 e are eachsupplied to a camera 45 e and 46 e, respectively, via double reflectionprisms 81.

[0081] The images obtained by the cameras 45 e and 46 e are supplied todisplays for a left eye and a right eye, respectively, of a first user.

[0082] A second user is supplied with images from the cameras 45 e′ and46 e′ which generate images of the partial beam bundles 19 e′ and 20 e′via an optical system which is disposed along the optical axis 5 e′mirrored at the beam divider 41 e. The components 77′, 78′, 79′, 80′ and81′ are similar to the corresponding components of the optical systemdisposed along the optical axis 5 e.

[0083] A stereo-examination system 1 f schematically shown in FIG. 10again serves to generate stereo-image pairs for two observers. Theexamination system 1 f is similar in construction to the examinationsystem shown in FIG. 9. It likewise comprises two prism systems 77 f and78 f which are adapted to be driven via a gear system 79 f about anoptical axis 5 f such that the prism system 77 f rotates about theoptical axis at twice the rotational speed as the prism system 78 f.Here, the prism system 78 f also feeds two partial beam bundles 19 f and20 out of a parallel beam bundle 13 f generated by an objective 3 f.However, the prism system 78 f serves to superpose the two partial beambundles 19 f and 20 f along the optical axis 5 f by means of deflectingprisms 83 and 84 and a beam coupler 83. In contrast to the embodimentshown in FIG. 9, the examination system if merely comprises a singlecamera 45 f which is likewise disposed on the optical axis 5 f togenerate representations of the image information contained in the twopartial beam bundles 19 f, 20 f. In order to separate the tworepresentations from each other, the prism system 78 f comprises aswitchable shutter 87 disposed in the beam path of the partial beambundle 20 f as well as a further switchable shutter 88 disposed in thebeam path of the partial beam bundle 19 f. The shutters 87 and 88 areliquid crystal shutters which are switchable, by means of a controller49 f, from a state in which they transmit light to a state in which theytransmit substantially no light. The controller 49 f, first, switchesthe shutter 87 to the light-impermeable state and the shutter 88 to thelight-permeable state so that the partial beam bundle 19 f is directedto the camera 45 f. The image of the object 8 f thus produced by thecamera 45 f is read out by the controller 49 f from the camera 45 f andrepresented by the same on a display 51 f for observation of the lefteye of a first observer. Subsequently, the controller 49 f switches theshutter 88 to the light-impermeable state and, correspondingly, theshutter 87 to the light-permeable state. As a result, the other partialbeam bundle 20 f is supplied to the camera, and the image thus recordedby the camera 45 f is read out by the controller 49 f and represented ona further display 52 f for the right eye of the user. This procedure isthen repeated so that the camera 45 f alternately records the imageinformation of the object 8 f kcontained in the partial beam bundles 19f and 20 f and represents the same on the displays 51 f and 52 f for theuser's left eye and the right eye, respectively. Due to the partial beambundles 19 f and 20 f being switched alternately in time, it is thuspossible to obtain the image information contained therein by merely onecamera.

[0084] There is a corresponding optical system provided for a seconduser, said optical system being disposed along an optical axis mirroredat the beam divider 41 f and having the same structure as the opticalsystem disposed along the optical axis extending through the beamdivider 41 f. For the sake of clarity, this optical system for thesecond user is not shown in full detail in FIG. 10.

[0085]FIG. 11 shows a plan view of a part of a stereo-examination system1 g. The examination system 1 g shown in FIG. 11 is similar to theexamination system shown in FIG. 7 in that it comprises more than threecameras, namely eight cameras, which are disposed at equal distance froman optical axis 5 g, the eight cameras being fixedly disposed spacedapart from each other in circumferential direction about the opticalaxis 5 g by the same distance. Each camera feeds a partial beam bundle19 g 1, . . . , 19 g 8 out of a parallel image-side beam bundle 13 g togenerate an image of the image information of an object contained in therespective beam bundles 19 g 1, . . . , 19 g 8 and to supply the same toa controller 49 g.

[0086] A pair of displays comprising two display apparatus 51 g and 52 gis connected to the controller 49 g for providing a stereoscopic displayfor a first observer. Correspondingly, there are two display apparatus51 g′ and 52 g′ connected to the controller 49 g for a second observer.The controller 49 g and the cameras cooperate as selection arrangementin that the controller 49 g selects a first pair of cameras from theeight cameras to allocate these selected cameras to the displays 51 g,52 g for the first user and to represent the images recorded by saidpair of cameras on the corresponding displays, if applicable, after animage rotation. The controller 49 g selects a second pair of cameras toallocate the same to the displays 51 g′ and 52 g′ for the second userand to represent the images recorded by said pair of cameras on thecorresponding displays, if applicable, after an image rotation.

[0087] In the situation depicted in FIG. 11, the controller 49 g hasallocated the camera receiving the partial beam bundle 19 g 1 to thedisplay 52 g and thus to the right eye of the first user. The camerareceiving the partial beam bundle 19 g 2 is allocated to the display 51g′ and thus to the left eye of the second user. And the camera receivingthe partial beam bundle 19 g 5 is allocated to the displays 51 g and 52g′ and thus to both the left eye of the first user and the right eye ofthe second user. Accordingly, the first user receives a stereoscopicrepresentation of the object under observation with a stereobasis whichis indicated in FIG. 11 by a line 91, while the second observer receivesa stereoscopic representation of the object with a stereobasis which isindicated in FIG. 11 by a line 92. Both lines or stereobases 91 and 92are disposed at different azimuth angles about the optical axis 5 g.These azimuth angles of the stereobases 91, 92 are variable by thecontroller 49 g. For example, the stereobasis for the first observer canbe rotated about the optical axis 5 g counter-clockwise in that thecontroller selects, instead of the camera receiving the partial beambundle 19 g 1, the camera receiving the partial beam bundle 19 g 8 forallocation to the display 52 g observed by the right eye of the firstuser so that a stereobasis 91 g′ results for this user which is shown inFIG. 11 as dotted line.

[0088]FIG. 12 schematically shows a further stereo-examination system 1h. It serves again to present stereoscopic pairs of images of an object8 h on displays 51 h and 52 h to a left eye and a right eye,respectively, of a first user and on displays 51 h′ and 52 h′ to a lefteye and a right eye, respectively, of a second observer. To this end,the examination system 1 h further comprises an objective 3 h forgenerating a parallel image-side beam bundle 13 h from a divergent beambundle 11 h emanating from the object 8 h and an imaging optical system93 for transmitting the parallel beam bundle 13 h to a CCD camera chip45 h so that a sharp image of the object 8 h is formed on the same.

[0089] In the beam path of the parallel beam bundle 13 h, there isprovided a switchable stop 87 h in a plane which corresponds to aFourier plane of the objective 3 h with respect to the object plane 7 hthereof. The stop 87 h is a liquid crystal stop having a plurality ofliquid crystal elements (pixels) which are switchable by the controller49 h from a state in which they transmit light to a state in which theytransmit less light. In the plane of the stop 87 h, the controller 49 hcomprises selected regions 19 h 1, 19 h 2, 19 h 3 and 19 h 4 whichcorrespond to partial beam bundles whose image information isrepresented on the displays 51 h to 52 h′ for the observers. Here, theregion 19 h 1 is allocated to the display 52 h and thus to the right eyeof the first user, the region 19 h 3 is allocated to the display 51 hand thus to the left eye of the first user, the region 19 h 2 isallocated to the display 51 h′ and thus to the left eye of the seconduser, while the region 19 h 4 is allocated to the display 52 h′ and thusto the right eye of the second user.

[0090] The camera 45 h records, sequentially in time, the imageinformation contained in the individual partial beam bundles forrepresentation on the displays 51 h to 52 h′. To this end, the stopelements or pixels of the LCD stop 87 h which are disposed outside ofsaid regions 19 h 1 to 19 h 4 are constantly switched to the state inwhich they transmit less light. Of the pixels disposed in the regions 19h 1 to 19 h 4, merely the pixels disposed in the region 19 h 1 areswitched, in the situation shown in FIG. 12, to the state in which theytransmit much light, while the pixels of the other regions 19 h 2, 19 h3 and 19 h 4 are switched to the state in which they transmit littlelight. Accordingly, the camera records in this switching sate the imageinformation contained in the partial beam passing through hecross-section of the region 19 h 1. The controller 49 h reads this imageinformation out of the camera 45 h and presents the same on the display52 h for the right eye of the first user.

[0091] Subsequently, the pixels contained in the region 19 h 1 areswitched to the state in which they transmit less light, while thepixels contained in the region 19 h 3 are switched to the state in whichthey transmit much light. Accordingly, the cross-section of the region19 h 3 is exposed for transmission of the corresponding partial beambundle, and the camera 45 h records the image information contained inthis partial beam bundle which is read out by the controller 49 h andpresented on the display 51 h for the left eye of the first observer.

[0092] Subsequently, the pixels of the LCD stop 87 h contained in theregion 19 h 3 are switched to the state in which they transmit lesslight. A corresponding procedure is then carried out for the regions 19h 2 and 19 h 4, i.e., first, a picture of the partial beam traversingthe cross-section of the region 19 h 2 is taken by the camera 45 h andrepresented on the display 51 h′ and, then, a corresponding picture istaken of the partial beam bundle traversing the region 19 h 4 andpresented on the display 452 h′ for the right eye of the secondobserver.

[0093] Accordingly, the first observer obtains as stereoscopicrepresentation of the object 8 h with a stereobasis which is indicatedin FIG. 12 by a line 91 h, while the second observer obtains astereoscopic representation with a stereobasis which is indicated by aline 92 h.

[0094] Herein the images recorded by the camera are rotated in theirimage planes by the controller before transmission to the displays 51 h,52 h and 51 h′, 52 h′, respectively, such that they are displayed to theobserver in their correct orientation. This is, inparticular, the case,if a direction of the stereobasis 19 h 1 and 19 h 2 is a horizontaldirection in the displayed images.

[0095] By use of the switchable stop 87 h as selector for selecting theindividual partial beam bundles to be imaged, particular degrees offreedom are obtained for the adjustment of the stereobases 91 h, 92 hfor the individual users. It is not only possible to displace thestereobases azimuthally about an optical axis 5 h in that the controller49 h selects regions which are displaced with respect to the regions 19h 1 to 19 h 4 in circumferential direction about the axis 5 h to switchthe same, successively in time, into their light-permeable state, whichresults into the stereobases 91 h, 92 h being rotated about the opticalaxis 5 h. Rather, it is also possible to change the lengths of thestereobases in that the distance between the regions 19 h 1 and 19 h 3and 19 h 2 and 19 h 4, respectively, is reduced. Moreover, it is alsopossible to displace the stereoscopic bases 91 h and 92 h in parallel.This results in that the respective observer perceives the object 8 h atthe same azimuth but at a different elevation.

[0096] The individually controllable liquid crystal switching elementsof the stop 87 h can be disposed periodically in a field in twodirections (X,Y) extending orthogonally to each other.

[0097] A variant thereof is schematically shown in FIG. 13. A swichtablestop 87 h comprises a plurality of liquid crystal elements which areindividually switchable. These elements comprise triangular elements 95,96, 97 and 98 as well as arcuate segments 99 defining a segmentedcircle. The segments 95, 96, 97, 98 and 99 are combined such that,together, they form a circular switchable stop. In order to open thestop allowing a partial beam bundle 19 h to pass therethrough, aplurality of the elements are switched by the controller into the satein which they transmit much light, as it is shown in FIG. 13 by thehatched elements, while all other elements are switched to the state inwhich they transmit little light.

[0098] A further variant of a switchable stop 87 h is shown in FIG. 14.This switchable stop 87 h, too, is of circular shape, the switchableelements being each of square shape and are distributed incircumferential direction about the optical axis 5 h in three annularrings. FIG. 14 shows two switchable elements in hatched outline which isto indicate that they are switched to the state in which they transmitmuch light in order to allow a partial beam bundle 19 h to passtherethrough, while all other switchable elements are switched to thestate in which they transmit little light.

[0099] A further variant of a switchable stop 87 h is illustrated inFIGS. 15 and 16. The stop 87 h shown in plan view in FIG. 15 comprises aplurality of switching elements 96 which are mechanically switchablebetween a state in which they are permeable to light and a state inwhich they are impermeable to light. Each switching element 96 comprisesa sector-shaped lamella 101 which is supported in a bearing 105 to berotatable about a rotational axis 103 and is driven by means of anactuating drive 107 controlled by the controller 49 h to rotate aboutthe axis 103. The plurality of lamellas 101 is disposed incircumferential direction about the optical axis 5 h, the rotationalaxis 103 of each lamella 101 being oriented radially with respect to theoptical axis 5 h, as it is shown in FIG. 15. The drives 107 of thelamellas 101 can change the orientation thereof about the axis 103 froma first position in which the lamellas 101 lie flat in the paper planeof FIG. 15 to a second position in which the lamellas 101 are orientedperpendicular to the paper plane of FIG. 15. In the fist position, thelamellas substantially prevent light from passing through, and in thesecond position, they substantially allow light to pass through. In FIG.15, a region 104 is shown in hatched outline in circumferentialdirection in which the lamellas 101 are in their secondlight-transmitting position, while all other lamellas 101 are in thefirst position in which they prevent light from passing through.Accordingly, the partial light bundle 19 h can freely pass through theregion 104. The controller can thus define different regions incircumferential direction for the passage of a partial beam bundle andswitch the same, successively in time, to the light-permeable state sothat the camera 45 h can record the image information contained in thispartial beam bundle.

[0100] In order to select the partial beam bundles imaged on the camera,the stereo-examination system shown in FIG. 12 comprises a switchabletransmission device, namely the switchable liquid crystal stop. However,it is also possible to provide a similar system with a switchablereflection device, as it is illustrated in FIG. 17. In thestereo-examination system ii schematically shown in this Figure, aparallel image-side beam bundle 13 i is deflected through 90° C. at apolarizing beam divider 109 and impinges as polarized parallel beambundle 3 i′ on a switchable mirror 111. The switchable mirror 111comprises a plurality of individual switchable mirror elements which areformed as liquid crystal elements. In a first switching state, theliquid crystal elements reflect the impinging radiation of the beambundle 3 i′ with a polarization such that the reflected radiation passesthrough the polarizing beam divider 109, while it reflects the radiationwith another polarization in a second switching state so that thereflected radiation does not pass through the polarizing beam divider109.

[0101] In the state shown in FIG. 17, a controller 49 i has determinedtwo regions 19 i 1 and 19 i 2 of the mirror 111 which are alternatelyswitched from the first switching state to the second switching state.All other regions of the mirror 111 remain permanently in the secondswitching state. In FIG. 17, a situation is shown in which the region 19i 1 is switched to the state in which the radiation reflected in thisregion passes through the polarizing beam divider 109 as partial beambundle 19 i 1′ and exposes a camera 45 i.

[0102] A method for adjusting a stereobasis of the stereo-examinationsystem will now be described in further detail with reference to FIGS.18 and 19.

[0103]FIG. 18 shows an operating room. An operating table 132, on whicha patient 133 lies on whom a microsurgery is being performed by asurgeon 135 is fixedly mounted on the floor 131 of the operating room. Amicroscope 138 is mounted to a stand 137 fixedly attached to the floor131 of the operating room such that it records images of an operatingfield 139 and visibly represents the same for the surgeon 135. To thisend, the surgeon 135 wears a head-mounted display apparatus 141comprising two displays 51, 52 which together present stereoscopicimages to the left eye and the right eye of the surgeon. The images tobe represented are transmitted wireless as data from the microscope 138mounted on the stand to the display apparatus 141. A preset fixed point151 of the microscope 138 is defined as point of origin of a polarcoordinate system. Moreover, at the display apparatus 141 of thesurgeon, there is defined a reference point 153, the position of whichrelative to the fixed point 151 is determined as an azimuth φ and anelevation u by a position detection apparatus 161 of the examinationsystem which is attached to the microscope 138 near the fixed point 151and shown in detail in FIG. 20.

[0104] An arrangement of a stereobasis 91 for the stereo-images providedfor the surgeon 135 is shown in plan view onto the XY-plane of theoperating room in FIG. 19. The fixed point 151 at the microscope 138 isselected such that, in plan view onto the XY-plane, it coincides withthe optical axis 5 of the microscope 138. The stereobasis for thesurgeon 135 shown as line 91 is oriented azimuthally such that aconnecting line between the reference point 153 of the surgeon 135 andthe fixed point 151 extends orthogonally to the line 91. If the surgeon135 moves in the operating room and, in so doing, changes his positionφ1 relative to the fixed point 151 in circumferential direction aboutthe optical axis 5, the controller 49 readjusts the stereobasiscorrespondingly such that the stereobasis continues to be disposedorthogonally to the connecting line between the surgeon 135 and theoptical axis 5. The surgeon 135 thus gets a stereoscopic imageimpression of the operating field 139 via the display apparatus 141which corresponds substantially to an image impression which the surgeon135 would obtain if he viewed through a stereomicroscope shown in FIGS.1 and 2 onto the operating field 139. However, the surgeon 135 is now nolonger obstructed in his freedom of movement around the operating field139 by the position of oculars of the stereomicroscope.

[0105] In particular, the examination system 1 can likewise obtain astereoscopic representation of the operating field 139 for a secondsurgeon, whose azimuthal position is indicated by 153′ in FIG. 19, via adisplay apparatus worn by the same, with a stereobasis 92 for thestereoscopic representation supplied to the second surgeon being adaptedto the azimuthal position φ₂ of the same in that the stereobasis 92 alsoextends orthogonally to a connecting line between the position 153′ ofthe second surgeon and the optical axis 5.

[0106] With reference to FIG. 20, the position detection apparatus 161is disposed symmetrically with respect to the optical axis 5 on themicroscope 138. It detects positions of one or more surgeons in theoperating room in the polar coordinate system φ, θ having its point oforigin at the fixed point 151. The position detection apparatus 161comprises a conical mirror 163 which reflects radiation impinging on themirror 163 from an angular range ±γ with respect to a horizontal plane165 onto an optical system 167 which images said radiation on a CCD chip169.

[0107] The surgeon 135 who carries a light source on his head islocatable in the operating room by the apparatus 161 because hisazimuthal position about the axis 5 as well as his elevation withrespect to the plane 165 in a range ±γ can be determined by evaluatingthe image of the CCD chip 169. If several surgeons are present in theoperating room, each surgeon may carry a light source, the lightintensity of which changes time-dependently, a different characteristictime pattern of the light intensity being provided for each surgeon. Byevaluating the image of the camera 169 and taking into consideration thedetected time patterns, it is thus possible to determine the positionsof the individual surgeons. The image of the camera 169 is evaluated bythe controller 49 which changes, corresponding to the detected positionof the respective surgeon, the stereobasis 91, 92 of the same inazimuthal direction about the optical axis 5 of the microscope 138.

[0108] The controller 49 can also react to changes in the elevation θ ofthe surgeon in that it shifts the stereobases in parallel, as it hasbeen described with reference to the embodiment shown in FIG. 12.

[0109] It is also possible to position the observer remote from theobject under observation if, for example, there is only space for a fewpeople at the operating table and further persons, for example, studentswish to observe the operation directly “flesh-and-blood”. These personcan then be positioned outside of the operating room. A fixed point andan orientation of his user coordinate system in space can be determinedfor each one of these persons so that, when viewing their head-mounteddisplay, they get the impression as if the region of the patient underobservation were disposed around this very, namely, their personal fixedpoint.

[0110]FIG. 21 is a schematic representation of a furtherstereo-examination system 1 j. Again, it comprises a microscopeobjective 3 j with an optical axis 5 j and an object plane 7 j forpositioning an object. The objective 3 j images the object to infinityso that a conic beam bundle emerging from the object plane 7 j at theoptical axis 5 j is converted into a parallel beam bundle. It impingeson a mirror 181 disposed behind the objective 3 j, said mirrorcomprising a mirror surface 183 which intersects the optical axis 5 j ata point 185. The mirror 181 is pivotal about this point 185 into twospatial directions, a drive 187 being provided for pivoting the mirror181.

[0111] The radiation reflected at the mirror surface 183 impinges on astop 189 with a central stop aperture 191.

[0112] If the mirror 181 is in the position shown in continuous outlinein FIG. 21, the stop aperture 191 is traversed by a partial beam bundle19 j′ which is generated from a partial beam bundle 19 j afterreflection at the mirror surface 183. The partial beam bundle 19 j isthe partial beam bundle, the central beam of which emanates from theobject 8 j at an angle a with respect to the optical axis 5 j.

[0113] The partial beam bundle 19 j′ impinges on a further mirror 193,the mirror surface 195 of which is disposed symmetrically to the mirrorsurface 183 of the mirror 181, the mirror surface 195 being pivotalabout a point 197 in two spatial directions. The point 197 disposed issymmetrically to the point 185 with respect to the plane of the stop189. In order to pivot the mirror 193, a drive 199 is provided which isshown merely symbolically in FIG. 21.

[0114] After having been reflected at the mirror surface 195, thepartial beam bundle 19 j′ passes through an imaging optical system 201and impinges as conic partial beam bundle 19 j″ on a light-sensitivesurface 45 j of a camera, the optical imaging system 201 being providedsuch that the object 8 j in the object plane 7 j is imaged on thelight-sensitive surface 45 j.

[0115] In the pivot position of the mirrors 181 and 193 shown in FIG.21, the camera 45 j thus records an image of the object 8 j viewed at anangle a to the optical axis.

[0116] The dotted lines in FIG. 21 show pivot positions of the mirrorsurfaces 183 and 195 in which a partial beam bundle 20 j which isdifferent from the partial beam bundle 19 j images the object 8 j on thecamera 45 j. A central beam of the partial beam bundle 20 j is inclinedat an angle −α to the optical axis 5 j.

[0117] The drives 187 and 199 are driven by a controller not shown inFIG. 21. By pivoting the mirror surfaces 183 and 195, this controllercan thus adjust within an adjustment range arbitrary viewing angles atwhich the object 8 is imaged on the camera 45 j. The controller can thussequentially read an image out of the camera 45 j at a first viewingangle and then change the position of the mirrors 181 and 193 and readan image out of the camera 45 j at a second viewing angle. The imagestaken at the first and the second viewing angles are then supplied tothe left eye and the right eye, respectively, of the user, so that hegets a stereoscopic impression of the object 8 j.

[0118] In the variant shown in FIG. 24, the distance and the pivotangles of the pivotal mirrors 181, 193 are adjusted to each other suchthat the first pivotal mirror 181 always directs the partial beam bundle191′, 201′ on a central region of the second pivotal mirror 193, and thesecond pivotal mirror 193 only images this central region as partialbeam bundle 191″, 201″ on the camera 451. To this end, the stop 189 ispositioned between the second pivotal mirror 193 and the camera 451.

[0119] In contrast to the above-described embodiment, in the embodimentshown in FIG. 25, the first pivotal mirror is replaced by a stationaryfacet mirror 180. The facets 182, 184 of the facet mirror 180 arearranged in pairs inclined at an angle relative to each other whichcorresponds to the pivot angle δ of the pivotal mirror 193.

[0120] As a result, partial beam bundles 19 m′, 20 m′ are alwaysdirected from every mirror facet 182, 184 to the second mirror 193provided as pivotal mirror which, depending on its pivotal position,selects one partial beam bundle from said plurality of partial beambundles 19 m′, 20 m′ and reflects the selected partial beam bundle 19 m″and 20 m″, respectively, in the direction of the camera 45 m, while theother partial beam bundles 20 m″ and 19 m″, respectively, are absorbedby the stop 189 m.

[0121] A further variant of the above-described embodiment isillustrated in FIG. 26. Instead of the facet mirror, this embodimentcomprises a prism arrangement 186 disposed in beam direction behind theobjective. The prism arrangement 186 consists of a ring of individualprisms 188, 190 each of which deflects a partial beam bundle 19 n′, 20n′ in axial direction. On the optical axis 5 n, there is again disposeda pivotal mirror 193 n which directs, in its different pivot positions,one of the partial beam bundles 19 n″ into the direction of the camera45 n, while the partial beam bundles 20 n″ are absorbed by the stop 189n positioned between the mirror 193 n and camera 54 n.

[0122] Further, FIG. 27 shows a variant of the two above-describedembodiments, wherein, instead of the one pivotal mirror 193 n and theone camera 45 n, there are disposed two of the kind. Here, the facets182, 184 of the facet mirror 180 (or, in a variant not shown, the prismsof a prism arrangement) are provided such that facets 182, 184 (orprisms) disposed opposite each other, each direct their partial beambundle 19 p′ and 20 p′, respectively, to different pivotal mirrors 193p′, 193 p″ and thus to different cameras 45 p′, 45 p″. Each of the twopivotal mirrors 193 p′, 193 p″ selects, according to its pivotalposition, a partial beam bundle 19 p′ and 20 p′ from the facets 182 and184 (or prisms) respectively allocated thereto so that each of thecameras 45 p′, 45 p″ always receives a partial beam bundle 19 p′, 20 p′for generating corresponding representations. The facets 182, 184allocated to the two pivotal mirrors 193 p′, 193 p″ are, moreover,positioned in alternate configuration in circumferential direction ofthe facet mirror 180. The variant shown in FIG. 27 comprises a facetmirror with 6 pentagonal facets which are disposed about a centralhexagon. The four of the six facets which do not lie in the plane of thethree mirror centers are each slightly bent upwards towards the center.The other two opposed facets lie approximately in a plane with thecentral hexagon. Each one of these flatly disposed facets is allocated,together with the two diagonally opposite, upwardly bent facets, to onepivotal mirror 193 p′, 193 p″, respectively. These pivotal mirrors 193p′ and 193 p″ each select, depending on the pivotal position, one ofthree facets and reflect the respective partial beam bundle 19′, 20′ inthe direction of the camera 45 p′ and 45 p″ respectively allocatedthereto.

[0123] In a further variant, not shown, the two individual movablepivotal mirrors 193 p′, 193 p″ are replaced by a single rotatablepolyeder mirror in the form of an irregular truncated pyramid. Dependingon the rotational position, said truncated pyramid provides two oppositemirror surfaces in the plane of the optical axis, each of which directsone of the two selected partial beam bundles to a camera.

[0124] In FIGS. 24 to 27, the respective controllers of the pivotalmirror drives are not shown.

[0125] In the embodiments comprising a plurality of cameras, the lattercan also by formed by different regions of a light-sensitive elements ofa single camera.

[0126] Finally, FIG. 28 shows an embodiment wherein one of the partialbeam bundles 19 q″ and 20 q″ is fed out by a turnable double stop 203having two stop apertures 205′, 205″. The rotation of the double stop203 is effected by a drive 207 which is controlled by a controller 221.Moreover, this embodiment comprises a rotating chopper wheel 209 with anuneven number of open sectors 223, here shown with three sectors. Thechopper wheel 209 is driven by the drive 211 which is likewisecontrolled by the controller 221. By rotation of the chopper wheel 209,the two stop apertures 205′, 205″ alternately overlap with the opensectors 223 of the chopper wheel 209. As a result, one of the partialbeam bundles 19 q′ and 20 q′ is alternately supplied to the camera 45 qand detected there so that the camera 45 q alternately receives imagesof a region 8 q of the object 7 q.

[0127] In order for the camera 45 q being maintained in correctsynchronization when the double stop 203 is rotated, a marking hole 213is furthermore provided in the double stop 203. A reference beam bundle217 emanating from the object 7 q passes through said hole, providedthat an open sector of the chopper wheel 209 is currently in acorresponding angular position, impinges on the deflecting mirror 215connected to the double stop 203 and is detected by the photo diode 219disposed on the optical axis 5 q.

[0128] Accordingly, the output signal of the photo diode 219 ismodulated with a frequency which is dependent upon the rotational speedand the number of sectors of the chopper wheel 209, the phase of saidmodulation being dependent upon the difference between the phases of thechopper wheel 209 and the double stop 203. The output signal of thephoto diode 219 is supplied to the controller 221, and the controller221 controls the drive 211 of the chopper wheel 209 such that a constantmodulation phase is maintained. As a result, the camera is correctlysynchronized with the chopper wheel 209 in every rotational position ofthe double stop 203 and thus provides a correctly alternating imagesequence.

[0129] A further variant of a selection arrangement for selectingdifferent partial beam bundles to image the object on a camera can beprovided by a stop which is rotatable about an axis and comprises adecentral stop aperture. The rotational axis of the stop coincides withthe optical axis of a microscope objective and, by rotating the stopabout the optical axis, an azimuth angle of the partial beam bundle canthen be selected which is imaged on a camera. As a result, a firstcamera image of the object can be recorded in a first rotationalposition of the stop about the optical axis, and a second camera imagecan be recorded in a different rotational position of the stop about theoptical axis. The two camera images are then supplied to the left eyeand the right eye, respectively, of the observer so that he gets astereoscopic impression of the object.

[0130] A similar embodiment of the stereo-examination system is shown inFIG. 29. Here, a mirror prism 225, driven by a drive 227, rotates abouta rotational axis which coincides with the optical axis 5 r. As aresult, the prism 225 always feeds with mirror surfaces 225′ and 225″another partial beam bundle 19 r′ out of the object-side beam bundle andpasses it on to the camera 45 r. The selection of specific partial beambundles 19 r″ is effected here by a pulsed light source 229, the timingof which can be controlled by the observer by means of the controller221 r. For example, a stroboscope lamp arrangement is provided ascontrollable pulsed light source 229. The lamp arrangement 229 is causedto effect a flash sequence of double the prism rotary frequency for eachobserver; the camera images corresponding to a flash sequence arealternately allocated to the two stereo-images for the respectiveobserver. The phase position between the different flash sequencesdetermines the angular difference between the stereobases for theobservers.

[0131] As against this, FIG. 30 shows an embodiment wherein a camera 45s, 46 s, 45 s′, 46 s″ is allocated to each one of the two eyes of twoobservers. The selection of the appertaining partial beam bundles iseffected here by dividing the beam bundle up between the two observes bythe cross beam divider 41 s; the latter furthermore causes the beambundle to be divided into the two partial beam bundles for the two eyesof the first observer. The division of the other beam portion for thetwo eyes of the second observer is effected by the beam divider 41 s′.Each one of the four cameras 45 s, 46 s, 45 s′, 46 s′ is associated witha stop 235 s, 236 s, 235 s′, 236 s′ which is rotatable about the opticalaxis 4 s and has a selection region 237 s, 238 s, 237 s′, 238 s′,respectively. The stops 235 s, 236 s and 235 s′, 236 s′ respectivelyallocated to an observer are each coupled such that they allowoppositely disposed partial beam bundles 19 s and 20 s to passtherethrough. The rotational positions of the stops 235 s, 235 s′ and236 s, 236 s′ respectively allocated to different observers, however,are freely selectable. The camera optics 15 s, 16 s, 15 s′ and 16 s′focus the partial beam bundles 19 s″ and 20 s″ respectively fed out.Each one of the observers can adjust the pair of stops 235 s, 236 s and235 s′, 236 s′ respectively allocated to the same by means of acontroller, not shown, such that the desired stereoscopic representationof the object 8 s is made available to him.

[0132]FIG. 22 shows, by way of example, an advantageous embodiment of anillumination for a stereo-examination system of the invention on thebasis of an embodiment which is similar to the embodiment shown in FIG.3. Light from a light source 211 is shaped by an optical system 231 toform a parallel beam 215 which impinges on a field 217 of symbolicallyrepresented micromirrors 219. The micromirrors 219 are controllable by acontroller 49 k which likewise causes cameras 45 k and 46 to rotateabout an optical axis 5 k of an objective 3 k to supply a stereoscopicrepresentation of an object 8 k positioned in the object plane 7 k ofthe objective 3 k to a left eye and a right eye of a user via displays51 k, 52 k. To this end, the camera 45 k feeds a partial beam bundle 19k out of the complete beam bundle which emanates from the object 8 kinclined at an angle α to the optical axis 5 k and is further processedby the objective 3 k. Equally, the other camera 46 k feeds out acorresponding partial beam bundle 20 k which is inclined at an angle −αto the optical axis 5 k.

[0133] The micromirrors 219 are selectively switchable by the controller49 k from a first switching state to a second switching state. In thefirst switching state, they reflect the light of the light source 211contained in the parallel beam 215 through 90° so that it is fed intothe beam path of the microscope via a mirror surface 43 k of a beamdivider 41 k and focussed onto the object 8 k via the objective 3 k. Inthe second switching state, the micromirrors 219 each reflect the lightof the beam 215 such that the beam is not fed into the beam path of themicroscope and, accordingly, the radiation of the lamp 211 does notreach the object 8 k.

[0134] The controller 49 k controls the micromirrors 219 such that notthe light of the entire cross-section of the beam 125 is used forilluminating the object 8 k. This is illustrated in further detail withreference to FIG. 23 which shows a cross-section through the objective 3k and an arrangement of the cross-sections of the partial beam bundle 19k and 20 k in the plane of the objective 3 k. The cross-sections of thepartial beam bundles 19 k and 20 k occupy only a portion of the entirecross-section of the objective 3 k. Those regions of the objective 3 kwhich are disposed outside of the cross-sections of the partial beambundles 19 k and 20 k are occupied by regions 225 which are traversed bythe radiation used to illuminate the object 8 k. This is achieved byappropriately controlling the micromirros 219. In the regions disposedoutside of the regions 225 of the cross-section of the objective 3 k, noradiation of the light source 211 passes through the objective 3 k. Bythis spatial separation of the cross-sectional regions of the objective3 k used for the illumination of the object 8 k and the imagining of thesame, disturbing reflections caused by the illumination in the images ofthe object 8 k recorded by the cameras 45 k and 46 k are eliminated.

[0135] The beam guidance for the illumination illustrated with referenceto FIGS. 22 and 23 can be applied to any other of the above-describedexamination systems to reduce reflections caused by the illuminationradiation in the recorded images.

[0136] A variant of the stereo-examination system shown in FIGS. 4 and 5can reside in that, instead of the cameras 45 a, 46 a and 45 a′, 46 a′,respectively, oculars are provided for direct observation by twoobservers. The observers then do not view the imaged object via separatedisplays, such as viewing screens, but in a similar way as describedwith reference to the conventional stereomicroscope shown in FIG. 2.However, an accordingly modified stereo-examination system isadvantageous in so far as each observer can rotate his pair of ocularsfreely about the optical axis and thus is no longer obstructed by thefixed arrangement in circumferential direction about the optical axis asit is the case with the conventional stereomicroscope shown in FIG. 2.

[0137] In this respect, it is possible to provide separate zoom systemsin a beam path between the respective beam divider and the oculars sothat each observer can select his own zoom position. The objective canthen be an objective with variable working distance.

[0138] In the embodiment described above with reference to FIGS. 18 and19, the fixed point 151 for the user coordinate system lies on theoptical axis. This is appropriate if the user is to perform directlymanipulations on the object 133 under observation, as it applies to thecase of the surgeon 135 in the operating room as shown in FIG. 18.

[0139] However, it is also possible for the user to be positioned remotefrom the object under observation so that the fixed point of the usercoordinate system does not coincide with the region of the object underobservation. An example for such an application would be a telesurgicalmethod wherein the surgeon is positioned distant from the patient andperforms the operation on the patient by means of a remote-controlledrobot. In this case, an image is defined between an azimuth of the userin the user coordinate system and an azimuth of the stereobasis aboutthe optical axis of the microscope is defined. By moving the head, theuser can then likewise obtain impressions of the object underobservation from different perspectives.

1. A stereo-examination system for imaging an object, or an intermediateimage generated from an object, comprising: an objective arrangementhaving an optical axis and an object plane for positioning the object tobe imaged, or the intermediate image, wherein the objective arrangementreceives an object-side beam bundle emanating from the object plane intoa solid angle region and converts the same into an image-side beambundle, a selection arrangement for selecting at least a pair of partialbeam bundles from the image-side beam bundle, and an image transmissionapparatus for generating representations of the images provided by theat least one pair of partial beam bundles, wherein the selectionarrangement is provided for displacing a beam cross-section of at leastone of the two partial beam bundles relative to a beam cross-section ofthe image-side beam bundle, a controller being provided for controllingthe selection arrangement to displace the beam cross-section of the atleast one partial beam bundle in a circumferential direction about theoptical axis.
 2. The stereo-examination system according to claim 1,wherein the selection arrangement is provided for selectively selectingonly a first partial beam bundle or only a second partial beam bundle ofthe pair of partial beam bundles from the image-side beam bundle.
 3. Thestereo-examination system according to claim 2, wherein the selectionarrangement comprises a switchable stop disposed in the beamcross-section of the image-side beam bundle, said stop selectivelytransmitting the first partial beam bundle or the second partial beambundle.
 4. The stereo-examination system according to claim 3, whereinthe switchable stop comprises a plurality of separately controllablestop elements which are switchable from a state in which they transmitlight to a state in which they substantially transmit no light.
 5. Thestereo-examination system according to claim 4, wherein the stopelements comprise liquid crystals.
 6. The stereo-examination systemaccording to claim 4, wherein the stop elements comprise mechanicallydisplaceable stop elements.
 7. The stereo-examination system accordingto claim 2, wherein the selection arrangement comprises a switchablemirror disposed in the beam cross-section of the image-side beam bundlewhich selectively reflects the first partial beam bundle or the secondpartial beam bundle.
 8. The stereo-examination system according to claim7, wherein the switchable mirror comprises a plurality of separatelycontrollable mirror elements which are switchable from a state in whichthey reflect light of the image-side beam bundle to the imagetransmission apparatus to a state in which they do not reflect saidlight to the image transmission apparatus.
 9. The stereo-examinationsystem according to claim 8, wherein the mirror elements comprise liquidcrystals.
 10. The stereo-examination system according to claim 8,wherein the mirror elements comprise mechanically displaceable mirrorelements.
 11. The stereo-examination system according to claim 2,wherein the selection arrangement comprises a stop fixedly positioned inthe beam cross-section of the image-side beam bundle and at least onecontrollable beam divider for selectively directing the first partialbeam bundle or the second partial beam bundle through the stop.
 12. Thestereo-examination system according to claim 2, wherein the imagetransmission apparatus comprises a camera, and wherein the controller isprovided to control the camera and the selection arrangement such thatthe camera generates, successively in time, at least one representationof the image provided by the first partial beam bundle and at least onerepresentation of the image provided by the second partial beam bundle.13. The stereo-examination system according to claim 12, wherein thecontroller is provided for controlling the selection arrangement suchthat the latter selects at least two pairs of partial beam bundles fromthe image-side beam bundle, and wherein the controller is furthermoreprovided for controlling the camera and the selection arrangement suchthat the camera generates, successively in time, at least onerepresentation of the image produced by each partial beam bundle of theat least two pairs of partial beam bundles.
 14. The stereo-examinationsystem according to claim 1, wherein the selection arrangement comprisesa pulsed light source.
 15. The stereo-examination system according toclaim 14, wherein the selection arrangement comprises a reflector whichis, in particular, displaceable about the optical axis.
 16. Thestereo-examination system according to claim 1, wherein the imagetransmission apparatus comprises at least a pair of cameras, whereineach camera is allocated to a partial beam bundle of the pair of partialbeam bundles to generate a representation of the image provided by saidpartial beam bundle.
 17. The stereo-examination system according toclaim 16, wherein the selection arrangement comprises the imagetransmission apparatus, and the two cameras are rotatable about arotational axis to displace the two selected partial beam bundlesrelative to the beam cross-section of the image-side beam bundle. 18.The stereo-examination system according to claim 16, wherein the twocameras are fixedly positioned relative to the objective arrangement,and the selection arrangement comprises two controllable beam deflectorsrespectively allocated to the two cameras to supply each of the twopartial beam bundles to the respectively allocated camera.
 19. Thestereo-examination system according to claim 16, wherein the two camerasare fixedly positioned relative to the objective arrangement, and theselection arrangement comprises an optical system rotatable about arotational axis to supply each of the two partial beam bundles to thecamera allocated thereto.
 20. The stereo-examination system according toclaim 19, wherein the rotatable optical system is an image-rotatingoptical system which comprises, in particular, a Dove prism or/and aSchmidt-Pechan prism.
 21. The stereo-examination system according toclaim 16, wherein a beam dividing arrangement for supplying theimage-side beam bundle to several selection arrangements is provided, aseparate image transmission apparatus being allocated to each selectionarrangement.
 22. The stereo-examination system according to claim 21,wherein the selection arrangement comprises a rotatable stop having adecentral aperture.
 23. The stereo-examination system according to claim21, further comprising an illumination apparatus for illuminating theobject through the beam dividing arrangement.
 24. The stereo-examinationsystem according to claim 1, wherein, in the direction of the opticalaxis, the selection arrangement comprises two controllable beamdeflectors and a stop, the stop being disposed between the twocontrollable beam deflectors or one of the two controllable beamdeflectors being disposed between the stop and the other one of the twocontrollable beam deflectors.
 25. The stereo-examination systemaccording to claim 1, wherein the selection arrangement comprises afacet mirror or a facet prism, a controllable beam deflector and a stop.26. The stereo-examination system according to claim 1, wherein theselection arrangement comprises a rotatable stop having two aperturesfor feeding-out of the two partial beam bundles and a rotatable chopperwheel comprising at least one light-impermeable region and at least onelight-permeable region for blocking out one of the fed-out partial beambundles.
 27. The stereo-examination system according to claim 1, whereinthe image transmission apparatus comprises at least three cameras,wherein a partial beam bundle is directed to each camera, said partialbeam bundle being fixed relative to the other cameras, and wherein theselector arrangement selects from the at least three cameras differentpairs for generating the representation to displace the at least onebeam cross-section about the optical axis.
 28. The stereo-examinationsystem according to claim 1, wherein the objective arrangement imagesthe object plane to infinity.
 29. The stereo-examination systemaccording to claim 1, wherein the objective arrangement images theobject plane to finity, and the selection arrangement is disposed in apupil plane of image-side beam bundle.
 30. The stereo-examination systemaccording to one of claims 1, wherein the selection arrangement isdisposed in a plane of the image-side beam bundle which is conjugatedwith respect to the object plane.
 31. The stereo-examination systemaccording to claim 1, wherein the image transmission apparatus comprisesa display apparatus for representing the image provided by the firstpartial beam bundle such that it is visible for a left eye of the user,and for representing the image provided by the second partial beambundle such that it is visible for a right eye of the user.
 32. Thestereo-examination system according to claim 31, wherein images providedby the first and second partial beam bundles are displayed such thatthey are rotated in their image planes.
 33. The stereo-examinationsystem according to claim 31, further comprising a position detectiondevice for detecting at least one azimuth of a position of the userrelative to the objective arrangement and for providing an azimuthsignal which is representative of the azimuth, the controller adjustingthe displacement of the at least one partial beam bundle dependent uponthe azimuth signal.
 34. The stereo-examination system according to claim33, wherein the image transmission apparatus is configured to displaythe images to be rotated in their image planes about an image rotationangle dependant on the azimuth signal.
 35. The stereo-examination systemaccording to claim 1, further comprising an illumination apparatuscomprising a beam coupler for superposing a cross-section of anillumination beam to the beam cross-section of the image-side beambundle, the illumination apparatus being controllable such that thecross-section of the illumination beam does substantially not overlapwith the beam cross-sections of the partial beam bundles.
 36. Thestereo-examination system according to claim 35, wherein theillumination apparatus comprises a field of a plurality of selectivelyswitchable mirrors.
 37. A stereo-image generation apparatus forgenerating at least a pair of representations of an object forobservation by at least one user, comprising: a detector arrangement fordetecting radiation emanating from a region of the object into at leasttwo solid angle regions and for providing radiation data correspondingto the detected radiation, a position detection apparatus for detectinga first position of the user relative to a fixed point in a usercoordinate system, a selection arrangement for determining the at leasttwo solid angle regions dependent upon an azimuth or/and an elevation ofthe user position in the user coordinate system, and a display apparatusfor displaying a first representation for a left eye of the user and fordisplaying a second representation for a right eye of the user dependentupon the radiation data.
 38. The stereo-image generation apparatusaccording to claim 37, wherein the detector arrangement and theselection arrangement comprise the stereo-examination system accordingto claim
 1. 39. A stereo-image generation method for generating at leasta pair of representations of an object for observation by at least oneuser, comprising: detecting a first position of the user relative to afixed point in a user coordinate system, detecting radiation emanatingfrom a region of the object into at least two solid angle regions andproviding radiation data corresponding to the recorded radiation,supplying the radiation data to a display and displaying a firstrepresentation for a left eye of the user and displaying a secondrepresentation for a right eye of the user, and subsequently: detectinga second position of the user relative to the fixed point and: if anazimuth of the second position has changed as compared to an azimuth ofthe first position: displacing at least one of the two solid angleregions azimuthally about an axis or/and if an elevation of the secondposition has changed as compared to an elevation of the first position:displacing at least one of that the two solid angle regionselevationally with respect to the axis.